1. Field of the Invention
This invention relates to a trunk line exchange system in an international communication network, and particularly relates to a trunk line exchange system capable of executing re-distribution of the number of international transmission lines for respective regions in the international communication network.
This application is based on Patent Application No. Hei 9-221610 filed in Japan, the content of which is incorporated herein by reference.
2. Background Art
Conventionally, in the international network which conducts the international exchange of the trunk lines, a fixed number of transmission lines are distributed so as to meet demand in each country (which is called a "region", hereinafter). The number of transmission lines for a region is determined by calculating a ratio of average traffic to busy hour traffic for each region and a fixed number of communication lines are normally allocated for each region. Moreover, the number of transmission lines for each region is normally includes spare lines in order to preserve efficient call connections even during busy hours.
In addition to the above line-allocation, another measure for busy hours has been provided in the conventional system, in which, an alternative or detour route is registered in advance in an international trunk line exchange apparatus, and, when the traffic density to a region exceeds 100% causing a congested condition, the trunk switching is executed for the region through the alternative route using a trunk line exchange apparatus located in a third region. An example of such measure is disclosed in Japanese Patent Application, First Publication No. 7-221833.
In the above described conventional trunk line exchange system, there are some drawbacks, in addition to the costly spare lines for preventing deterioration of call connections in a congested condition, in that, as shown in FIG. 4, even if an activity ratio of a trunk line for a busy region is nearly 100%, lines in another region are inactive due to the time difference, which results in reducing the average employment efficiency of trunk lines in the whole trunk line exchange system, which may be designated a transmission resource.
When an alternative route is used during congested hours, since it is necessary to carry out a series of operations of recalling and searching the alternative route, that is, operations of calling and recalling to acquire a line to the destination and, if line is busy, operations are required to search and acquire an alternative line, the processing of the trunk line exchange system is increased which sometimes exceeds a capacity of the system or renders the system more restricted by addition of the processing to the normal processing during a busy period.
It is, therefore, the object of the present invention to provide a system capable of enabling the efficient utilization of the transmission resource and capable also of avoiding an exchange apparatus at any region from falling into congestion.